Lonwijk moves to Kenilworth Road on a season-long loan.
The deal could become permanent if "certain criteria" are met. Lonwijk played for new Luton boss Matt Bloomfield during a previous loan with Wycombe Wanderers.
Bloomfield told the Luton website: “We had Nige for a few months at the end of season before last at Wycombe and he was fantastic for us. I tried to get him back last summer but we didn’t have as much money as Huddersfield at that point, so I couldn’t get him, but he’s someone who we think highly of.
“He’s had a bit of a stop-start season last year and he’s not quite hit the heights that we all believe he can get to, but he’s got a really high ceiling and is another great lad.
“He’s got good versatility and can play anywhere in the back four or back five, and has incredible athleticism, he’s really good on the ball and we’re really pleased to give him a home.”